1. Field of the Invention
This invention relates generally to connections between lengths of pipe, or between pipes and fittings. More particularly, the invention is directed toward a device and method of connecting two lengths of pipe in a restrained joint configuration, while employing a locking segment that is self-braking to prevent over-rotation and penetration of a spigot.
2. Description of Related Art
Due to thrust forces, earth movement, and external mechanical forces exerted on pipes, the industry has focused substantial attention on the problem of maintaining connections between adjacent lengths of pipe after installation. The result of this attention is a library of differing solutions and approaches known in the art. The majority of these solutions can be categorized into either xe2x80x9cpush-onxe2x80x9d joints or xe2x80x9cmechanical joints.xe2x80x9d
Push-on solutions are exemplified by U.S. Pat. No. 2,953,398, and account for the majority of straight-run pipe connections. In a typical configuration, a spigot end of a pipe slides into a bell end of another pipe past a tightly fitted gasket. A variation of the push-on joint is evidenced by U.S. Pat. No. 2,201,372, to Miller, which employs a compression snap-ring fitted within a special lip of the bell, in order to exert pressure onto locking segments and thus drive them into the spigot, restraining the joint against thrust forces. U.S. Pat. No. 3,445,120, to Barr, likewise employs a gasket with stiffening segments completely encased therein that are generally disposed such that they and the gasket may roll between a locking and a free position. As the Barr gasket rolls under extraction forces, it is intended eventually to encounter a position in which the stiffened plane needs to compress for further rolling, in theory terminating the rolling and restraining the joint.
Other examples of restrained push-on joints include U.S. Pat. Nos. 5,295,697; 5,464,228; and 5,067,751. The securement of the connection in such references is effected by locking segments or wedges within the gasket that engage the spigot. The locking segments possess a groove that mates with an annular rib on the bell, such that the rib acts as a rocker, or cam, or during some movements, as a wedge. During insertion of the spigot into the bell, the segments rotate on the rib, but are prevented from appreciable straight-line movement by the mating of the rib and groove. Upon experiencing counter-forces tending to effect removal of the spigot, the rib acts as a cam, both causing the segments to pivot on the rib as an axis, and exerting a radially inward pressure as the segment attempts to slide past the rib.
A locking segment for use in a restrained joint avoids over-rotation and penetration of the inserted spigot by muring between two surfaces in the bell, thus arresting rotation before positions are reached in which pressures on the spigot would result in likely penetration. The segment therefore can rotate to an effective locking degree, upon which rotation the radial forces by which the segment bites into the pipe increase. By virtue of the muring that prevents rotation beyond a desired maximum, a graph of the relationship between a radial force exerted by the segment on the spigot, in relation to the thrust force experienced could show a radial force that generally increases as thrust forces increase, but only up to a given point. At that point, the line representing radial force could be made to substantially plateau. By selection of materials and configurations, the plateau may be fixed below a spigot penetration value.
The following stated objects of the invention are alternative and exemplary objects only, and no one or any should be read as required for the practice of the invention, or as an exhaustive listing of objects accomplished.
As suggested by the foregoing discussion, an exemplary and non-exclusive alternative object of this invention is to provide a locking segment that is capable under certain conditions of self-braking, to prevent over-rotation or other un-capped increases in radially inward pressure as thrust forces increase.
A further exemplary and non-exclusive alternative object is to provide a joint in which a locking segment is capable of selectively converting a portion of thrust forces into radially inward pressures, up to a maximum radial pressure that is thereafter unaffected by increasing thrust forces.
A further exemplary and non-exclusive alternative object is to provide a joint that counters extraction of a spigot by distributing thrust forces into opposing axial forces in the bell, and a radial force between bell and spigot that has a maximum, which is below the magnitude of force that would fail the spigot.
A further exemplary and non-exclusive alternative object is to provide an effective restrained joint that resists over-penetration of the spigot.
The above objects and advantages are neither exhaustive nor individually or collectively critical to the spirit and practice of the invention, except as stated in the claims. Other or alternative objects and advantages of the present invention will become apparent to those skilled in the art from the following description of the invention.